The present invention relates to an automatic transmission control system for cars comprising a variable-speed drive enabling the velocity ratio of an input and output shaft to be varied continuously. On transmissions of the aforementioned type, the variable-speed drive is normally operated by an actuator controlled by an electronic control system on the basis of engine and vehicle operating parameters. It also includes a gear lever with a number of settings, at least one of which enables the actuator to receive electric signals from the control system for activating the variable-speed drive. When the gear lever is so set, the velocity ratio best suited to the operating conditions of the engine and the vehicle is selected automatically according to the strategy memorised on the electronic control system, with no possibility of it being modified directly by the driver of the vehicle. Transmissions of the type briefly described above present a number of drawbacks.
Foremost of these is that, under certain driving conditions, the velocity ratio selected by the variable-speed drive may not always provide for optimum vehicle performance and consumption. Moreover, engine braking is ineffective, due to the time required to achieve a substantial reduction in the velocity ratio.